JSON: use odata.kind values "Entity" and "deletedEntity", Atom: use metadata:link and metadata:deleted-link

The current naming of the odata.kind values "Entry", "deletedEntry", and "linkEntry" in JSON reflects the "Atom-origin" of the OData formats.

We now consistently use of "entity" when speaking in OData terminology and use "entry" only when intentionally using the Atom terminology, so it is odd to have Atom terminology in the new JSON format. Also different parts of the JSON document use different values, unintentionally reflecting the change history of this concept.

To increase consistency between JSON and Atom the OData-specific "link" and "deletedLink" are better represented using medata:link and metadata:deleted-link without the suffix "-entry". This is also more consistent with Atom as these OData-specific elements reflect changes to the atom:link element.